Hydro Lettuce

jbarNovember 26, 2011

First of all, congratulations for all the information present in this forum and the always helpful attitude.

I managed to assemble a NFT system from scratch which holds 12 adult plants + 12 seedlings. This is not a highly controlled environment. Only an hack to play with hydroponics and to see what i can grow. It seems to work reasonable well.

I've read most of the information in this forum regarding hydroponics, however, after successfully growing two crops, I have some questions that maybe you can help.

The system is composed by three PVC pipes with holes on top (see pictures 5 and 6 ). Plants grow from the holes directly without any medium. Seeds are started in a pot with rock wool and then moved to the NFT. One of the pumps moves water to the pipes while the other circulates the water in the reservoir and aerates the nutrient solution. The nutrient solution is a 5 part element which I add every time I change the solution (every two weeks). I acquire the nutrients in powder from a professional nutrient supplier.

Nutrients are set at 1.5-1.7mS, PH adjusted between 6 and 6.5 with Sodium Bisulfite. I know Sodium is not so good, but the nutrient solution is buffered and I only have to adjust PH 1-2 times before the solution is changed. Pumps run in intervals of 30m on, 15m off during the day and every hour during the night. The reservoir has 40 liters.

Currently i'm growing Wattercress and Lettuce (Grand Rapids) and I manage to get a crop of Lettuces in 50-60 days (weather varying).

My questions:

Why some lettuces get some strange marks? It is a Magnesium deficit? They grow normally but always have some leaves with those strange marks (See picture 8).

Why plants starting dying when at the sun? The air temperature is 12C. At night they look healthy again. This reminds my they are unable to absorb enough water. Nutrients running too high?

I understand your point and you may be right. However, pumps do not run continuously, so all roots will be exposed to air for some time. From what I see, if they are exposed for too long, they become brown and are pruned automatically. With time, all healthy roots are the ones in contact with the nutrient film.

What is curious is that most lettuces only develop long roots, while some develop dense, short roots. The point is why? Also, it seems that the ones with longs roots develop slower.

Are you doing hydroponics or aeroponics? What media Are you using? I'm using coconut coir and perlite. The problems we are running into is the lettuce is wilting too fast after being harvest and the size is not too big. What kind of mix nutrients are you using?I'm living in Florida now

I would think it has to be nutrient strength. I experimented and documented carefully the results. The best mix was 1/4 the first couple weeks and then on to 1/2 strength max. It also lasted for several weeks without noting deficiencies. They do not require alot. I documented it in my blog and on the videos on YOUTUBE if that helps.

I agree with halfway. I grew several types of lettuces in DWC hydro, and found that a weak solution works best with lettuces. I also found they liked less light and warmth then fruiting plants such as tomatoes and peppers.